Gas Distribution System For Ceramic Showerhead of Plasma Etch Reactor

ABSTRACT

A gas delivery system for a ceramic showerhead includes gas connection blocks and a gas ring, the gas connection blocks mounted on the gas ring such that gas outlets in the blocks deliver process gas to gas inlets in an outer periphery of the showerhead. The gas ring includes a bottom ring with channels therein and a welded cover plate enclosing the channels. The gas ring can include a first channel extending ½ the length of the gas ring, two second channels connected at midpoints thereof to downstream ends of the first channel, and four third channels connected at midpoints thereof to downstream ends of the second channels. the cover plate can include a first section enclosing the first channel, two second sections connected at midpoints thereof to ends of the first section, and third sections connected at midpoints thereof to ends of the second sections. The channels are arranged such that the process gas travels equal distances for a single gas inlet in the gas ring to eight outlets in the cover ring allowing equal gas flow.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.13/118,933, filed on May 31, 2011, the entire content of which isincorporated herein by reference.

BACKGROUND

The Bosch process is a plasma etch process that has been widely used tofabricate deep vertical (high aspect ratio) features (with depth such astens to hundreds of micrometers), such as trenches and vias, in thesemiconductor industry. The Bosch process comprises cycles ofalternating etching steps and deposition steps. Details of the Boschprocess can be found in U.S. Pat. No. 5,501,893, which is herebyincorporated by reference. The Bosch process can be carried out in aplasma processing apparatus configured with a high-density plasmasource, such as an inductively coupled plasma (ICP) source, inconjunction with a radio frequency (RF) biased substrate electrode.Process gases used in the Bosch process for etching silicon can besulfur hexafluoride (SF₆) in an etching step and octofluorocyclobutane(C₄F₈) in a deposition step. The process gas used in the etching stepand the process gas used in the deposition step are respectivelyreferred to as “etch gas” and “deposition gas” hereinbelow. During anetching step, SF₆ facilitates spontaneous and isotropic etching ofsilicon (Si); during a deposition step, C₄F₈ facilitates the depositionof a protective polymer layer onto sidewalls as well as bottoms of theetched structures. The Bosch process cyclically alternates between etchand deposition steps enabling deep structures to be defined into amasked silicon substrate. Upon energetic and directional ionbombardment, which is present in the etching steps, any polymer filmcoated in the bottoms of etched structures from the previous depositionstep will be removed to expose the silicon surface for further etching.The polymer film on the sidewall will remain because it is not subjectedto direct ion bombardment, thereby, inhibiting lateral etching.

One limitation of the Bosch process is roughened sidewalls of etcheddeep features. This limitation is due to the periodic etch/depositionscheme used in the Bosch process and is known in the art as sidewall“scalloping”. For many device applications, it is desirable to minimizethis sidewall roughness or scalloping. The extent of scalloping istypically measured as a scallop length and depth. The scallop length isthe peak-to-peak distance of the sidewall roughness and is directlycorrelated to the etch depth achieved during a single etch cycle. Thescallop depth is the peak to valley distance of sidewall roughness andis correlated to the degree of anisotropy of an individual etching step.The extent of scallop formation can be minimized by shortening theduration of each etch/deposition step (i.e. shorter etch/depositionsteps repeated at a higher frequency).

In addition to smoother feature sidewalls it is also desirable toachieve a higher overall etch rate. The overall etch rate is defined asa total depth etched in a process divided by a total duration of theprocess. The overall etch rate can be increased by increasing efficiencywithin a process step (i.e. decreasing dead time).

FIG. 1 illustrates a conventional plasma processing apparatus 100 forprocessing a substrate 120 comprises a substrate support 130 and aprocessing chamber 140 enclosing the substrate support 130. Thesubstrate 120 may be, for example, a semiconductor wafer havingdiameters such as 4″, 6″, 8″, 12″, etc. The substrate support 130 maycomprise, for example, a radio frequency (RF) powered electrode. Thesubstrate support 130 may be supported from a lower endwall of thechamber 140 or may be cantilevered, e.g., extending from a sidewall ofthe chamber 140. The substrate 120 may be clamped to the electrode 130either mechanically or electrostatically. The processing chamber 140may, for example, be a vacuum chamber.

The substrate 120 is processed in the processing chamber 140 byenergizing a process gas in the processing chamber 140 into a highdensity plasma. A source of energy maintains a high density (e.g.,10¹¹-10¹² ions/cm³) plasma in the chamber 140. For example, an antenna150, such as the planar multiturn spiral coil shown in FIG. 1, anon-planar multiturn coil, or an antenna having another shape, poweredby a suitable RF source and suitable RF impedance matching circuitryinductively couples RF energy into the chamber to generate a highdensity plasma. The RF power applied to the antenna 150 can be variedaccording to different process gases used in the chamber 140 (e.g. etchgas containing SF₆ and deposition gas containing C₄F₈). The chamber 140may include a suitable vacuum pumping apparatus for maintaining theinterior of the chamber 140 at a desired pressure (e.g., below 5 Torr,preferably 1-100 mTorr). A dielectric window, such as the planardielectric window 155 of uniform thickness shown in FIG. 1, or anon-planar dielectric window (not shown) is provided between the antenna150 and the interior of the processing chamber 140 and forms a vacuumwall at the top of the processing chamber 140. A gas delivery system 110can be used to supply process gases into the chamber 140 through aprimary gas ring 170 or center injector 180 below the dielectric window155. Details of the plasma processing apparatus 100 in FIG. 1 aredisclosed in commonly-owned U.S. Patent Application Publication Nos.2001/0010257, 2003/0070620, U.S. Pat. No. 6,013,155, or U.S. Pat. No.6,270,862, each of which is incorporated herein by reference in itsentirety.

Gas delivery systems designed for fast gas switching are disclosed incommonly-owned U.S. Pat. Nos. 7,459,100 and 7,708,859 and U.S. PatentPublication Nos. 2007/0158025 and 2007/0066038, the disclosures of whichare hereby incorporated by reference.

The substrate 120 preferably comprises a silicon material such as asilicon wafer and/or polysilicon. Various features such as holes, viasand/or trenches are to be etched into the silicon material. A patternedmasking layer (e.g. photoresist, silicon oxide, and/or silicon nitride)having an opening pattern for etching desired features is disposed onthe substrate 120.

One problem of the apparatus 100 of FIG. 1 is that the primary gas ring170 is located closer to the periphery of the substrate 120 than to thecenter, which increases etch rate due to the time needed for completereplacement of one process gas to another process gas over the surfaceof the substrate 120 and can lead to process non-uniformity due to gaspressure non-uniformity across the substrate during processing.

SUMMARY

Described herein is a gas delivery system useful for supplying processgas to a ceramic showerhead for an inductively coupled plasma processingapparatus wherein semiconductor substrates supported on a substratesupport are subjected to plasma etching, the ceramic showerheadincluding radially extending gas inlets extending inwardly from an outerperiphery thereof, the gas delivery system comprising gas connectionblocks adapted to attach to the ceramic showerhead such that a gasoutlet of each of the blocks is in fluid communication with a respectiveone of the gas inlets in the ceramic showerhead and a gas ring havingequal length channels therein and gas outlets in fluid communicationwith downstream ends of the channels, each of the gas outlets beinglocated on a mounting surface supporting a respective one of the gasconnection blocks.

BRIEF DESCRIPTION OF FIGURES

FIG. 1 shows a conventional plasma processing apparatus.

FIG. 2 shows a plasma processing apparatus according to a preferredembodiment.

FIGS. 3A-D show details of the lower plate 270 wherein FIG. 3A is aperspective view of an upper surface thereof, FIG. 3B is a perspectiveview of the lower surface thereof, FIG. 3C is a bottom view thereof,FIG. 3D is a cross sectional view thereof.

FIGS. 4 A-H show details of the upper plate 280, wherein FIG. 4A is aperspective view of an upper surface thereof, FIG. 4B is a perspectiveview of a lower surface thereof, FIG. 4C is a side view thereof, FIG. 4Dis a cross sectional view thereof, FIG. 4E is a view of Detail E in FIG.4D, FIG. 4F is a view of Detail F in FIG. 4E, FIG. 4G is a crosssectional view at a gas connection location along the line G-G in FIG.4H and FIG. 4H is an end view of Detail H in FIG. 4C.

FIGS. 5A-B show the upper plate 280 mounted on the lower plate 270,wherein FIG. 5A is a perspective top view and FIG. 5B is a crosssectional view through the assembly shown in FIG. 5A.

FIGS. 6A-C show details of a gas connection block which supplies processgas to the ceramic showerhead wherein FIG. 6A is a perspective frontview of the block, FIG. 6B is a perspective back view of the block andFIG. 6C is a bottom view thereof.

FIGS. 7A-C show details of a gas ring, wherein FIG. 7A is a top view ofthe gas ring, FIG. 7B is a perspective view of the gas ring and FIG. 7Cshows details of the gas ring with a cover plate separated from a bottomring.

FIGS. 8A-D show details of the gas ring mounted on the ceramicshowerhead, wherein FIG. 8A is a perspective view of the gas ringsurrounding the showerhead, FIG. 8B shows how the shoulder screws of thegas connection block engage openings in fasteners fitted in mountingholes in the showerhead, FIG. 8C shows the shoulder screws inserted intothe radially extending mounting holes in the outer periphery of theshowerhead and the fasteners fully inserted in the showerhead, and FIG.8D is a perspective cross section of a gas connection block attached tothe gas ring and the showerhead.

DETAILED DESCRIPTION

The plasma processing apparatus described herein can achieve higher etchrates with greater uniformity than the conventional apparatus 100described above.

According to an embodiment, as shown in FIG. 2, a plasma processingapparatus 200 for processing a substrate 220 comprises a substratesupport 230 and a processing chamber 240 enclosing the substrate support230. The substrate 220 may be, for example, a semiconductor wafer havingdiameters of 8 inches, 12 inches or larger. The substrate support 230may comprise, for example, a radio frequency (RF) powered electrode. Thesubstrate support 230 may be supported from a lower endwall of thechamber 240 or may be cantilevered, e.g., extending from a sidewall ofthe chamber 240. The substrate 220 may be clamped to the substratesupport 230 either mechanically or electrostatically.

The substrate 220 is processed in the processing chamber 240 byenergizing a process gas in the processing chamber 240 into a highdensity plasma. A source of energy generates and maintains a highdensity (e.g., 10¹¹-10¹² ions/cm³) plasma in the chamber 240. Forexample, an antenna 250, such as the planar multiturn spiral coil shownin FIG. 2, a non-planar multiturn coil, or an antenna having anothershape, powered by a suitable RF source and suitable RF impedancematching circuitry inductively couples RF energy into the chamber togenerate a high density plasma. The RF power applied to the antenna 250can be maintained at the same power level or varied according todifferent process gases used in the chamber 240 (e.g. etch gascontaining SF₆ and deposition gas containing C₄F₈), during cycles ofalternately supplying the etch gas or disposition gas preferably withina time period of less than about 1 s, more preferably less than about200 ms. The chamber 240 is evacuated by a suitable vacuum pumpingapparatus for maintaining the interior of the chamber 240 at a desiredpressure (e.g., below 5 Torr, preferably 1-500 mTorr). The pressure canbe maintained at the same level or varied during the etching anddeposition cycles.

The chamber includes a ceramic showerhead 260 of uniform thickness isprovided between the antenna 250 and the interior of the processingchamber 240 and forms a vacuum wall at the top of the processing chamber240. A gas delivery system 210 can be used to supply process gas intothe chamber 240 through gas passages in the showerhead 260. The gasdelivery system 210 alternately supplies etch gas or deposition gas intothe chamber via fast switching valves (such as valve model numberFSR-SD-71-6.35, available from Fujikin of America, located in SantaClara, Calif.) which open and close within 40 milliseconds, preferablywithin 30 milliseconds. The valves can be on-off valves which do notdirect the deposition gas to a bypass line while the etch gas issupplied to the showerhead or vice versa. Fast gas switching valvesprovide faster switching than MFC valves which can take 250 millisecondsto stabilize before opening or closing.

In a preferred embodiment, the showerhead is a two-piece ceramicshowerhead comprising an upper plate 280 and lower plate 270 (describedlater with reference to FIGS. 3A-D and 4 A-H) made of an electricallyinsulating ceramic material, such as alumina, silicon nitride, aluminumnitride, a doped silicon carbide, quartz, etc. To prevent plasma fromigniting in the showerhead gas holes, the gas holes preferably havediameters of no greater than 0.06 inch and aspect ratios of at least 2.For example, the lower plate 270 can have a thickness of at least 0.2inch, preferably 0.2 to 1 inch. The vertical distance (chamber gap)between a bottom surface of the lower plate 270 and the substrate 220can be varied by moving the substrate support in a vertical direction toadjust the chamber gap in which plasma is generated between theshowerhead plate and the substrate.

The substrate 220 preferably comprises a silicon material such as asilicon wafer and/or polysilicon. Various features such as holes, viasand/or trenches are to be etched into the silicon material. A patternedmasking layer (e.g. photoresist, silicon oxide, and/or silicon nitride)having an opening pattern for etching desired features is disposed onthe substrate 220.

Compared to the conventional plasma processing apparatus 100 with sidegas injection, the plasma processing apparatus 200 can more rapidly anduniformly switch the process gas in the chamber gap from the etching gasto the disposition gas and vice versa. In one embodiment wherein thesubstrate 220 has a diameter of 300 mm and the chamber gap is greaterthan 4 inches, the apparatus 200 can essentially completely switch (e.g.at least 90%) the process gas in a plenum between the upper and lowerplates within about 200 milliseconds and essentially completely switch(e.g. at least 90%) the process gas in the chamber gap within about 700milliseconds. Such rapid gas switching enables a significant increase inthe etching rate of openings in silicon using the plasma processingapparatus 200 to over 10 μm/min and depending on the critical dimension(CD) of features being etched the etch rate can be higher than 20 μm/minwhereas with side gas injection which provides etch rates of about 3μm/min.

FIGS. 3A-D show details of the lower plate 270 wherein FIG. 3A is aperspective view of an upper surface thereof, FIG. 3B is a perspectiveview of the lower surface thereof, FIG. 3C is a bottom view thereof, andFIG. 3D is a cross sectional view thereof.

As shown in FIGS. 3A-D, the lower plate 270 includes a planar lowersurface 302 and a stepped upper surface 304 which is thicker in acentral portion 306 thereof and thinner in an outer portion 308 thereof,two rows of axially extending gas holes 310 located in an annular zone312 on the outer portion 308 and extending between the upper and lowersurfaces 304,302. The lower surface 302 includes a step 320 in an outerportion thereof and includes an annular vacuum sealing surface 314 whichis vacuum sealed to a temperature controlled wall of the plasma chamber.The lower plate 270 includes an annular inner vacuum sealing surface 316and an annular outer vacuum sealing surface 318 on the upper surface 304on either side of the annular zone 312. A blind hole 322 is located onthe upper surface of the central portion 306 for mounting a temperaturesensor which monitors the temperature of the lower plate 270.

The thick central portion 306 efficiently dissipates heat to the ambientatmosphere above the exposed upper surface of the central portion 306.The outer edge of the showerhead can be set to an elevated temperatureto offset temperature gradients across the showerhead. One or morethermal gaskets 506 can be used to promote thermal transfer between theouter portion 308 of the lower plate 270 and the overlying plate 280.The lower plate 270 is exposed to most of the heat and vacuum loads andwill experience high thermal stress. By providing the complicated gasfeed conduits in the upper plate 280, there is less risk of breakage dueto thermal stresses during plasma processing of substrates in thechamber. Further, since the upper and lower plates are held together byvacuum force and sealed by O-rings, it is easy to periodically removeand clean these two parts. To provide erosion resistance, plasma exposedsurfaces of the lower plate can be coated with yttria.

In a chamber designed to process 300 mm wafers, the lower plate 270 iswider than the wafer and the vacuum sealing surface 312 engages a matingsealing surface on the top of the chamber 240. For example, the lowerplate 270 can have a diameter of about 20 inches, a thickness of about1.5 inches at the central portion 306 and a thickness of about 0.8 inchat the outer portion 308, the gas holes 310 being arranged in two rowsof gas holes including an inner row of 32 gas holes having diameters ofabout 0.04 inch and located about 5 inches from a center of the lowerplate 270 and an outer row of 32 gas holes having diameters of about0.04 inch and located about 6.5 inches from the center of the lowerplate 270, and the sealing surface 314 located on the step 320 in thelower surface 302, the step 314 having a depth of about 0.4 inch and awidth of about 1.2 inches.

FIGS. 4 A-H show details of the upper plate 280, wherein FIG. 4A is aperspective view of an upper surface thereof, FIG. 4B is a perspectiveview of a lower surface thereof, FIG. 4C is a side view thereof, FIG. 4Dis a cross sectional view thereof, FIG. 4E is a view of Detail E in FIG.4D, FIG. 4F is a view of Detail F in FIG. 4E, FIG. 4G is a crosssectional view of the upper plate at a gas connection mounting surfaceand FIG. 4H is a side view of the mounting surface.

The upper plate 280 is an annular plate of ceramic material having aplanar upper surface 402, a planar lower surface 404, an inner surface406 and an outer surface 408. A plurality of radially extending gaspassages 410 extend inwardly from the outer surface 408 and a pluralityof axially extending gas passages 412 extending from the lower surface404 to the radially extending gas passages 410. The annular upper plate280 is configured to surround the central portion 306 of the lower plate270 and overlie the upper surface 304 of the outer portion 308 of thelower plate 270 such that the axially extending gas passages 412 of theupper plate 280 are in fluid communication with an annular plenum 414 influid communication with the axially extending gas holes 310 in thelower plate 270.

For processing 300 mm wafers, the upper plate 280 is dimensioned to matewith the lower plate 270 and includes a plurality of radially extendinggas passages 410 supplying the gas holes 310 in the lower plate 270. Forexample, the upper plate 280 can include 8 radially extending gaspassages 410 having diameters of about 0.125 inch and located 45° apart,8 axially extending gas passages 412 having diameters of about 0.125inch and located about 5.75 inches from the center of the upper plate270, the annular plenum 414 having a width of about 1.7 inches and depthof about 0.015 to 0.02 inch, an inner O-ring groove 416 and an outerO-ring groove 418 surrounding the annular plenum 414. Depending onprocess requirements, the lower plate 270 can include a differentarrangement of gas holes 310 such as more or less than 64 gas holes inany desired pattern and with any desired geometry and dimensions.

To supply process gas to the gas passages 410, the upper plate 280includes mounting holes for attaching gas connection mounting blocks.The mounting holes include 8 pairs of axially extending mounting holes420 and 8 pairs of radially extending mounting holes 422. The holes 420have diameters of about 0.4 inch, are located about 0.5 inch from theouter edge of the upper surface 402 of the upper plate 280 and extendthrough the upper plate 280 to the lower surface 404. The mounting holes422 have diameters of about 0.35 inch, are located in flat mountingsurfaces 424 on outer periphery 408 of the upper plate 280, and extendinto the holes 420. The centers of each pair of the mounting holes 420,422 are located about 1 inch apart. The upper plate 280 and lower plate270 are preferably made of high purity alumina and the lower surface ofthe lower plate 270 includes a coating of high purity yttria coveringall of the lower surface except the sealing vacuum surface 314.

FIGS. 5A-B show the upper plate 280 mounted on the lower plate 270,wherein FIG. 5A is a perspective top view and FIG. 5B is a crosssectional view through the assembly shown in FIG. 5A. The mounting holes420 on the upper plate receive fasteners 504 which permit attachment ofeight gas connection blocks (not shown) to the outer surface 408 of theupper plate 280. The gas blocks deliver process gas to eight gasconnection locations 502 at which the process gas flows into the eightradially extending gas passages 410. By feeding the process gas from theouter surface 408 at equally spaced locations, fast gas switching can beachieved in the chamber. The gas volume of the annular plenum 414between the upper and lower plates is preferably less than 500 cm³ whichallows fast changeover from etch to deposition gases. The thick centralportion 306 of the lower plate 270 allows heat dissipation and thermallyconductive gaskets 506 between the opposed surfaces of the upper andlower plates allow the outer portion 308 of the lower plate 270 to bemaintained at a desired temperature. The lower plate 270 is exposed tomost of the heat and vacuum loads and will experience high thermalstress. Thus, it is desirable to minimize features on the lower platewhich might induce thermal fracture. With the two piece design, thecomplicated machined features that might induce thermal fracture arelocated on the upper plate 280. The upper and lower plates are notbolted together but rather are held together only by vacuum force andvacuum sealed with two O-ring seals located in the O-ring grooves416,418. This mounting arrangement allows easy disassembly for cleaningof the upper and lower plates.

With the plasma processing apparatus 200 described above, the gasdelivery system is operable to alternately supply an etching gas and adeposition gas to the plenum and replace the etching gas in the plenumbetween the upper and lower plates with the deposition gas within 200milliseconds or replace the deposition gas in the plenum with theetching gas within 200 milliseconds. The plasma processing apparatus canbe used to etch silicon on a semiconductor substrate supported on asubstrate support at a rate of at least 10 μm/min. The plasma processingapparatus is operable to essentially completely switch process gas inthe plenum within 200 milliseconds and in a plasma confinement zone(chamber gap) in the processing chamber from the etching gas to thedeposition gas or vice versa within about 500 ms.

In the preferred embodiment, the etching gas is SF₆ and the depositiongas is C₄F₈. In operation, the gas supply system does not divert theetching gas to a vacuum line during supply of the deposition gas to theplenum and does not divert the deposition gas to a vacuum line duringsupply of the etching gas to the plenum. Processing of a substrate usingthe plasma processing apparatus described above preferably comprises (a)supporting the substrate in the chamber, (b) supplying the etching gasto the plenum and flowing the etching gas through the gas holes in thelower plate into the chamber gap, (c) energizing the etching gas in thechamber into a first plasma and processing the substrate with the firstplasma, (d) supplying the deposition gas to the plenum so as tosubstantially replace the etching gas and flowing the deposition gasthrough the gas holes in the lower plate into the chamber gap, (e)energizing the deposition gas in the chamber into a second plasma andprocessing the substrate with the second plasma, (f) repeating steps(b)-(e) with a total cycle time of no greater than 1.8 seconds.

The etching gas preferably replaces at least 90% of the deposition gasin the chamber gap within a period of about 500 milliseconds in step(b), and the deposition gas preferably replaces at least 90% of theetching gas in the chamber gap within a period of about 500 millisecondsin step (d). During the process, pressure in the plenum is at least 5Torr during steps (b)-(e). During a cycle of supplying the etching gasand deposition gas, a total time of supplying the etching gas can be 1.3seconds or less and a total time of supplying the deposition gas can be0.7 seconds or less.

Chamber pressure can be adjusted such that pressure in the chamber gapduring supply of the etching gas is greater than 150 mTorr and pressurein the chamber gap during supply of the deposition gas is less than 150mTorr. In a preferred process, the etching gas is supplied to the plenumat a flow rate of at least 500 sccm and the deposition gas is suppliedto the plenum at a flow rate of less than 500 sccm. Preferably, thechamber gap between the substrate and the lower plate is greater than 4inches. During the supply of the etching gas the substrate can besubjected to plasma etching of high aspect ratio openings with pressurein the chamber gap maintained at less than 150 mTorr for 200milliseconds during a polymer clearing phase of the etching step and atover 150 mTorr for the remainder of the plasma etching step. During thesupply of the deposition gas the second plasma can deposit a polymercoating on sidewalls of the openings with pressure in the chamber gapmaintained at less than 150 mTorr for the entire deposition step. Theetching gas can be one or more of SF₆, CF₄, XeF₂, NF₃, Cl containing gassuch as CCl₄ and the deposition gas can be one or more of C₄F₈, C₄F₆,CHF₃, CH₂F₂, CH₄, C₃F₆, CH₃F.

The etching gas can be supplied through a first valve to eight etch gaslines which deliver the etching gas to the gas inlets in the outerperiphery of the upper plate wherein the eight etch gas lines have equalconductance. Likewise, the deposition gas is supplied through a secondvalve to eight deposition gas lines which deliver the deposition gas tothe gas inlets wherein the eight deposition gas lines have equalconductance. Fast acting valves can be used wherein fast acting solenoidvalves upon receiving a signal from a controller send pneumatic air to afast switching valve within 10 milliseconds and total time to open orclose the fast switching valve can be 30 milliseconds or less.

FIGS. 6A-C show an exemplary gas connection block 600 made of corrosionresistant metallic material such as stainless steel or polymer materialfor supplying process gas to one of the radially extending gas passage410 in the upper plate 280. FIG. 6A is a perspective front view, FIG. 6Bis a perspective rear view and FIG. 6C is a bottom view of theconnection block 600. The connection block 600 includes a mountingsurface 602 which contacts the flat mounting surface 424 such that a gasoutlet 604 in the mounting surface 602 aligns with the gas passage 410.A pair of bores 606 are aligned with holes 422 in the flat face 424 anda pair of shoulder screws 608 are slidable in the bores 606 in adirection away from the surface 602 such that press fitted plasticsleeves 609 on the shoulder screws 608 enter the holes 422 to positionthe block 600 on the upper plate 280. Circlips 611 at opposite ends ofthe bores 606 prevent the shoulder screws from falling out of the bores606. An O-ring groove 612 in the surface 602 around the gas outlet 604receives a gasket such as an O-ring to provide a seal between the block600 and the flat mounting surface 424 on the upper plate 280. A pair ofmounting holes 610 extend through flanges 607 to mount the block 600 ona gas delivery ring. The block 600 includes a mounting surface 613 witha gas inlet 615 therethrough and an O-ring groove 617 around the inlet615. Shallow rectangular recesses 619 reduce thermal transfer betweenthe block 600 and the gas delivery ring.

FIGS. 7 A-C show details of a gas delivery ring 700. FIG. 7A shows thering 700 with the eight gas connection blocks 600 mounted thereon, eachblock 600 providing fluid communication between the interior of theblock and the gas inlet 410 in the upper plate 280. FIG. 7B showsdetails of the gas ring 700 without the blocks 600 mounted thereon. Thegas ring 700 includes eight gas outlets 702 in an upper cover plate 704,a bottom ring 706 having channels therein enclosed by the upper cover704, a gas inlet 708 through which process gas enters the ring 700, andan extension limiter 710 connecting ends 712 of the bottom ring oppositethe gas inlet 708. As shown in FIG. 7C, the cover plate 704 includesinterconnected sections wherein a first section 714 extends ½ thediameter of the ring 706, a pair of second sections 716 each attached atits midpoint to a respective end of the first section 714 and extending¼ the diameter of the ring 706 and four third sections 718 each attachedat its midpoint to a respective end of one of the second sections 716 toposition the eight gas outlets 702 equal distances apart. The bottomring 706 includes interconnected channels therein wherein a firstchannel 720 extends ½ the diameter of the ring 706, a pair of secondchannels 722 each connected at its midpoint to a respective end of thefirst channel 720 and extending ¼ the diameter of the ring 706 and fourthird channels 724 each connected at its midpoint to a respective end ofone of the second channels 722. The cover plate 704 includes an L-shapedsection 726 attached to the middle of the first section 714. TheL-shaped section covers an L-shaped channel 728 in a gas inlet section730 of the lower ring 706, the channel 728 connecting the gas inlet 708to the first channel 720. The bottom ring 706 includes mounting holes732 in mounting surfaces 734, the holes 732 aligning with the holes 610in a respective one of the eight gas connection blocks 600.

The cover plate 704 and bottom ring 706 are preferably made from acorrosion resistant metallic material such as stainless steel or polymermaterial and the cover plate 704 can be sealed to the lower ring 706 bya suitable manufacturing process such as electron beam welding. Theinner and/or outer surfaces of the cover plate and/or bottom ring can becoated with a protective material such as a silicon coating. A preferredsilicon coating is “SILCOLLOY 1000”, a chemically vapor deposited (CVD)multilayer silicon coating available from SilcoTek, located inBellefonte, Pa. Details of suitable CVD silicon coatings can be found inU.S. Pat. No. 7,070,833, the disclosure of which is hereby incorporatedby reference. Although dimensions can vary depending on the size of theshowerhead and gas inlet arrangement, in a preferred embodiment thechannels 720/722/724 in the bottom ring 706 can be about 0.1 inch wideand about 0.32 inch high, the gas outlets 702 can be located on a radiusof about 10.4 inches. The cover plate 704 can be slightly wider than thechannels in the bottom ring and fit within a recess at the top of eachchannel. For example, the first, second and third sections 714/716/718can have a thickness of about 0.03 inch and a width of about 0.12 inch.As shown in FIG. 7C, ends 736 of the third sections 718 of the coverring 704 can be angled inwardly and include rounded ends 738. Therounded ends 738 can have a diameter of about 0.32 inch and openingsforming the gas outlets 702 can have a diameter of about 0.19 inchcentered in the rounded ends 734.

To avoid sudden changes in direction between the channels 720/722/724,the two connections between the ends of the first channel 720 and themiddle of the second channels 722 are preferably rounded with a radiusof about 0.13 inch and the four connections between the ends of thesecond channels 722 and the middle of the third channels 724 are roundedwith a radius of about 0.13 inch. In some portions of the bottom ringthere is a single channel (such as portions of the first channel 720 andportions of the third channels 724), two adjacent channels (such asportions where the first and third channels are concentric, the firstand second channels are concentric or the second and third channels areconcentric), or three adjacent channels (where the first, second andthird channels are concentric).

The gas ring 700 is preferably circular but other configurations arepossible if the ceramic showerhead has a different shape. To attach thegas ring 700 to the showerhead, the extension limiter 710 is loosenedand the gas ring is positioned around the upper plate 280. After theshoulder screws 608 are engaged with the holes 422 and the gas passages616 sealed in fluid communication with the gas inlets 410, the extensionlimiter 710 is fastened such that the ends 712 of the gas ring 700 areconcentrically aligned.

FIG. 8A is a perspective view of the gas ring 700 attached to the upperplate 280 of the showerhead 260 via the gas connection blocks 600. FIG.8B illustrates how the shoulder screws 608, which slide in bores 606 inthe gas connection blocks 600, fit in horizontal openings in fasteners504 which extend into mounting holes 420 in the upper plate 280. Asshown in FIG. 8C, the shoulder screws 608 include plastic bushings 609to minimize abrasion with the horizontal holes 422 in the ceramic upperplate 280. When the shoulder screws 608 are inserted into the holes 422in the flat mounting surface 424 on the outer periphery of the upperplate 280, ends of the shoulder screws 608 enter the openings in thefasteners 504 to hold the block 600 in position. Screws 614 mounted inholes 610 fasten the gas connection blocks 600 to the gas ring 700. Asshown in FIG. 8D, each gas connection block 600 includes an L-shapedpassage 616 connecting the outlet 702 of the gas ring 700 to an inlet ofone of the radially extending gas passages 410 in the upper plate 280.An O-ring in the O-ring groove 612 surrounds the outlet 604 of theL-shaped passage 616 to provide a seal between the gas connection block600 and the flat mounting surface 424 on the upper plate 280. Likewise,an O-ring in O-ring groove 617 provides a seal between the gasconnection block 600 and the mounting surface 734 on the gas ring 700.

Assembly of the gas ring 700 to the upper plate 280 requires the gasconnection blocks 600 to be attached to the gas ring 700 using thescrews 614, the gas ring 700 is spread open and slid over the upperplate 280, the fasteners 504 are fully inserted into the vertical holes420 with the openings in the fasteners 504 aligned with the openings422, the gas ring is closed around the upper plate 280 and the plate 710is tightened to prevent the ring from opening, and the screws 608 areinserted into the holes 422 and through the openings in the fasteners504. The fasteners 504 are preferably made of plastic and hold theblocks 600 in position around the showerhead.

With the gas ring 700, the process gas can be supplied through a singleinlet and delivered along equal length flow paths to the outlets 702whereby the pressure or flow rate of the gas ejected from each of theoutlets 702 are the same and the gas is uniformly ejected from eachoutlet. Thus, the flow passage resistance (conductance) from each of theoutlets can be made equal. As mentioned above, the number of outlets andchannels can be adapted to as needed and need not be restricted to eightoutlets or the particular channel arrangement described above.

In this specification, the word “about” is often used in connection witha numerical value to indicate that mathematical precision of such valueis not intended. Accordingly, it is intended that where “about” is usedwith a numerical value, a tolerance of 10% is contemplated for thatnumerical value.

While the plasma processing apparatus operable to quickly switch processgas has been described in detail with reference to specific embodimentsthereof, it will be apparent to those skilled in the art that variouschanges and modifications can be made, and equivalents employed, withoutdeparting from the scope of the appended claims.

1-17. (canceled)
 18. A gas delivery ring configured to supply processgas to an outer periphery of a showerhead of a plasma processingapparatus wherein a semiconductor substrate supported on a substratesupport is subjected to plasma processing, the gas delivery ringcomprising: a gas ring having a single gas inlet, a plurality ofchannels and a plurality of gas outlets in fluid communication with thegas inlet via the channels; the channels including a first channelconnected to the gas inlet at a midpoint thereof with downstream ends ofthe first channel equidistant from the gas inlet and from each other,two second channels connected at midpoints thereof to the downstreamends of the first channel with downstream ends of the second channelsequidistant from the downstream ends of the first channel and from eachother, and four third channels connected at midpoints thereof todownstream ends of the second channels with downstream ends of the thirdchannels connected to the gas outlets.
 19. The gas delivery ring ofclaim 18, comprising a bottom ring and cover ring, the channelsextending into an upper surface of the bottom ring and enclosed by thecover ring.
 20. The gas delivery ring of claim 18, wherein an uppersurface of the gas delivery ring includes mounting surfaces havingmounting holes therein configured to receive fasteners of gas connectionblocks which attach the gas delivery ring to the outer periphery of theshowerhead.
 21. The gas delivery ring of claim 18, wherein the gasdelivery ring includes free ends equidistant from the midpoint of thefirst channel.
 22. The gas delivery ring of claim 21, wherein anextension limiter connects the free ends of the gas delivery ring. 23.The gas delivery ring of claim 19, wherein the gas outlets are in anupper surface of the cover ring.
 24. The gas delivery ring of claim 19,wherein surfaces of the channels are coated with a silicon coating. 25.The gas delivery ring of claim 18, wherein the channels are rounded atlocations where the ends of the first channel are connected to midpointsof the second channels and where the ends of the second channels areconnected to the third channels, and downstream ends of the thirdchannels are angled inwardly and include rounded ends.
 26. The gasdelivery ring of claim 18, wherein the gas inlet is on an outerperiphery of the gas delivery ring and an L-shaped channel extendsbetween the gas inlet and the midpoint of the first channel.
 27. The gasdelivery ring of claim 19, wherein the cover ring is welded to thebottom ring, the gas outlets are located on a radius of about 10 to 11inches from a center of the gas delivery ring, the channels arerectangular in cross section with a width of about 0.1 inch and heightof about 0.32 inch, the cover ring has a thickness of about 0.03 inchand is located in a recess in an upper surface of the bottom ring, therecess having a width of about 0.12 inch along opposite sides of thechannels.
 28. A gas connection block adapted to provide a gas connectionbetween a gas delivery ring and a showerhead of a plasma processingapparatus wherein a semiconductor substrate supported on a substratesupport is subjected to plasma processing, the gas connection blockcomprising: a bottom mounting surface having a gas inlet therein; a sidemounting surface having a gas outlet therein; a gas passage extendingbetween the gas inlet and the gas outlet, the gas inlet adapted toreceive gas from the gas delivery ring and the gas outlet adapted tosupply the gas to the showerhead.
 29. The gas connection block of claim28, further comprising mounting holes in the bottom mounting surfaceadapted to receive fasteners which attach the gas connection block tothe gas delivery ring.
 30. The gas connection block of claim 28, furthercomprising first and second bores extending through the side mountingsurface on opposite sides of the gas outlet, the bores configured toreceive first and second shoulder screws which can be movably mounted inthe bores such that ends of the shoulder screws engage fasteners mountedin mounting holes in the showerhead.
 31. The gas connection block ofclaim 28, wherein the side mounting surface includes an O-ring grooveadapted to receive an O-ring therein for providing a gas seal around thegas outlet.
 32. The gas connection block of claim 28, wherein the bottommounting surface includes an O-ring groove adapted to receive an O-ringtherein for providing a gas seal around the gas inlet.
 33. The gasconnection block of claim 28, wherein the bottom mounting surfaceincludes recesses configured to reduce thermal transfer between the gasconnection block and the gas delivery ring.
 34. The gas connection blockof claim 29, wherein the mounting holes are located in flanges onopposite sides of the gas inlet.
 35. The gas connection block of claim30, further comprising shoulder screws mounted in the bores.
 36. The gasconnection block of claim 35, wherein the shoulder screws are retainedin the bores by circlips mounted in the bores.
 37. The gas connectionblock of claim 28, wherein the gas passage is an L-shaped passage.